A sniper does not necessarily mean a gun itself. A sniper is basically a highly trained marksman. The proper word for the gun is a sniper rifle. Which is a very powerful rifle with a scope designed for snipers.

Noob: I'm going to buy that sniper. (he's gonna buy the person)

Other dude: No don't you mean a sniper rifle?
Noob: Shut up noob.
Other dude: ...

A sniper is a cigarette butt that hasn't been entirely smoked. They are mainly smoked whenever you are out of cigarettes and are desperate for nicotine. You can find them in ashtrays inside your home and ashtrays outside of restaurants

I am craving so fucking bad!!! I think I am going to dig through my ashtray and find a nice sniper to smoke.